In recent years, three-cylinder engines are manufactured in order to overcome limitations of four-cylinder four-cycle combustion engines about improvement in fuel efficiency, an engine size, a reduction in weight, etc.
In terms of configuration, a three-cylinder engine consists of three cylinders, each of which has the same bore, stroke, and valve timing. The three cylinders of the three-cylinder engine include various devices required for combustion, as in four-cylinder engines. The intake/exhaust timing during combustion in each cylinder is controlled by an engine electronic control unit (ECU).
The three-cylinder engine applies a four-cycle combustion process of intake-compression-explosion-exhaust, or a two-cycle combustion process of intake/exhaust-compression/explosion.
The three-cylinder engine is controlled by a single cycle combustion process in which all of the three cylinders are controlled by a four-cycle combustion process, or two of the three cylinders are controlled by a four-cycle combustion process.
However, since the three-cylinder engine has structural characteristics in which bores, strokes, and valve timings of the respective cylinders are equal to one another, the engine generates noise and vibration compared to typical four or more cylinder engines. To resolve this, it is necessary to devise a design technique for three-cylinder engines in which a three-cylinder engine combines a four-cycle with a two-cycle. In addition, since engine performance (for example, power and torque) is deteriorated when this combined cycle engine is controlled, merchantable quality of the engine may be lowered.
The deterioration of NVH and engine performance is caused because the two- and four-cycle combustion cylinders have the same displacement even though the two-cycle engine has poor combustion efficiency compared to the four-cycle engine.